The present invention relates generally to mobile network communication systems, and more particularly to a system and method for creating logical radio link control (RLC) and medium access control (MAC) protocol data units (PDUs) for the long term evolution (LTE) layer-2 protocol stack.
The third generation partnership project (3GPP) has introduced the LTE system as an effective solution to the increasing performance requirements of mobile broadband communications. The LTE radio interface and radio network architecture ensures a high data transfer rate, reduced latency, data packet optimization, and improved system capacity and coverage. The LTE system offers an evolved universal terrestrial radio access network (E-UTRAN) as an air interface. The E-UTRAN includes several evolved Node-Bs (eNBs), also referred to as base stations (BS) or access points, that are distributed across multiple cells typically having one eNB per cell. Each eNB communicates with multiple user equipments (UEs) located within the coverage area. The uplink and downlink communication between the eNBs and the UEs is enabled by a user plane protocol stack that can be divided into first and second layers L-1 and L-2, respectively.
The first layer L-1 is the physical layer used for transmitting user information over the air interface. The first layer L-1 is connected to the second layer L-2 through a set of transport channels and receives the user information for transmission from the transport channels. The second layer L-2 includes media access control (MAC), radio access control (RLC), and packet data convergence protocol (PDCP) sub-layers that transform user data into a form fit for physical transmission. User data received by the PDCP sub-layer is converted into several PDCP PDUs that are stored in a PDCP transmission buffer. The PDCP PDUs are transmitted to the RLC sub-layer. The RLC sub-layer receives the PDCP PDUs from the PDCP sub-layer and processes the PDCP PDUs to generate RLC PDUs, which are stored in a RLC transmission buffer. The processing of the PDCP PDUs entails segmentation of the PDCP PDUs and then concatenation of the segmented PDCP PDUs to form RLC PDUs of uniform size and in addition to a RLC header for each of the RLC PDUs. The RLC sub-layer transmits the RLC PDUs to the MAC sub-layer, which in turn processes the RLC PDUs to generate MAC PDUs. The MAC PDUs are stored in a MAC transmission buffer from which they are transmitted to the physical layer.
The transmission of the user data for processing through the various sub-layers of the second layer L-2 of the user plane protocol stack requires that the user data be in the form of PDUs to be copied from the transmission buffer of the first sub-layer to the transmission buffer of the second sub-layer. For example, during the transmission of the PDCP PDUs from the PDCP sub-layer to the RLC sub-layer, the PDCP PDUs are copied from the PDCP transmission buffer to the RLC transmission buffer.
Such repeated data movement at each sub-layer requires several central processing unit (CPU) cycles for completion. This CPU effort is duplicated and increases as the size of the PDUs increases at each subsequent layer. Since the CPU is involved in the data movement, the cumulative maximum achievable throughput by the LTE L-2 protocol stack across all UEs on a target platform is effected, considerably reducing the efficiency of the LTE system. If the LTE system supports limited size contiguous buffer allocation and the limited size is less than the maximum RLC PDU or MAC PDU size supported by the LTE L-2 standard, then the system limitation also translates into a feature limitation of the LTE L-2 protocol stack in which all the features offered by the LTE L-2 standard are not exploited.
Therefore, it would be advantageous to have a system and method for creating PDUs at each sub-layer of the LTE L-2 protocol stack that eliminates the repeated movement of data at the RLC and MAC sub-layers, removes any limitation on the size of the PDUs created, and that overcomes the above-mentioned limitations of conventional systems for creating PDUs.